1. Field of the Invention
The present invention relates to a film containing an integral tear strip and to a method for producing a tear strip for a plastic film during the manufacture of the film itself.
2. Discussion of the Prior Art
Prior attempts to provide preferential tear lines for plastic materials, particularly plastic films, have involved the steps of mechanically processing the material to provide perforations or score lines therein along which the material may easily separate. Providing weakened areas such as these requires additional processing of the film and additional equipment costs which naturally adds to the overall cost of film production. In addition, providing perforations in a material is an undesirable manner of introducing a weakness line since the material itself penetrates into the perforations and does not entirely provide an acceptable product.
Another method for providing a line of weakness in a plastics film is to laminate a material having substantially different properties to an underlying substrate material which has preferential tear properties in a predetermined direction. The material which is then laminated thereon is provided with a high relative strength in its longitudinal direction so that it may remain substantially intact. By pulling on the laminated material, it tears the substrate material. The difficulty with providing a tear line using this technique is that additional process steps are required to laminate additional materials on a substrate material so that the processing cannot be conveniently done in line during the manufacture of the underlying plastic substrate.